The urethane U-cup design provides an excellent heavy-duty seal for either piston or rod applications. Urethane U-cups work well in both static and dynamic applications. The non-symmetric styles (MPI and MRO) provide the added benefits of: reduced seal movement, added stability in static applications and protection of the dynamic lip during installation. The rod style provides improved sealability on the I.D., while the piston style provides improved sealability on the O.D.